A malocclusion is a misalignment of teeth or incorrect relation between the teeth of the two dental arches. The term was coined by Edward Angle, the “father of modern orthodontics,” as a derivative of occlusion, which refers to the way opposing teeth meet. Angle based his classifications of malocclusions on the relative position of the maxillary first molar. According to Angle, the mesiobuccal cusp of the upper first molar should align with the buccal groove of the mandibular first molar. The teeth should all fit on a line of occlusion, which is a smooth curve through the central fossae and cingulum of the upper canines, and through the buccal cusp and incisal edges of the mandible. Any variations therefrom results in malocclusion.
There are three classes of malocclusions, Class I, II, and III. Further, class II is subdivided into three subtypes:
Class I: Neutrocclusion Here the molar relationship of the occlusion is normal or as described for the maxillary first molar, but the other teeth have problems like spacing, crowding, over or under eruption, etc.
Class II: Distocclusion (retrognathism, overjet) In this situation, the upper molars are placed not in the mesiobuccal groove but anteriorly to it. Usually the mesiobuccal cusp rests in between the first mandibular molars and second premolars. There are two subtypes:
Class II Division 1: The molar relationships are like that of Class II and the anterior teeth are protruded.
Class II Division 2: The molar relationships are class II but the central incisors are retroclined and the lateral incisors are seen overlapping the central incisors.
Class III: Mesiocclusion (prognathism, negative overjet) In this case the upper molars are placed not in the mesiobuccal groove but posteriorly to it. The mesiobuccal cusp of the maxillary first molar lies posteriorly to the mesiobuccal groove of the mandibular first molar. This malocclusion is usually seen when the lower front teeth are more prominent than the upper front teeth. In such cases, the patient very often has a large mandible or a short maxillary bone.
Orthodontics, formerly orthodontia (from Greek orthos “straight or proper or perfect”; and odous “tooth”) is that specialty of dentistry that is concerned with the study and treatment of malocclusions. Orthodontics treats malocclusion through the movement of teeth, as well as control and modification of facial growth, and occasionally in severe cases, through surgery.
Dental braces (also known as orthodontic braces, or simply braces) are commonly used to align and straighten teeth. In this approach, the braces provide a continuous static force to the teeth via an archwire connected to brackets affixed to each tooth. As the teeth slowly migrate due to the force, the force is dissipated. The archwires are then adjusted to add additional force and to continue the desired tooth movement. Although effective, this widely practiced orthodontic treatment takes about twenty-four months on average to achieve success. Furthermore, treatment time cannot be shortened by increasing the force due to pain and risk of root resorption from the excess force. The long treatment time, associated pain and the unpleasant aesthetics discourage patients from using such treatment. Indeed, some studies show that 75 percent of Americans could benefit from orthodontic treatment, yet remain untreated.
The aligner in contrast, is a clear molded device designed with the aid of computer modeling and that applies a continuous static force to the teeth. A series of aligners are designed to progressively move the teeth to a desired position. Because the device is transparent, it is more aesthetically appealing, and it is popular with teen and adult users. However, since the device can be taken off, treatment times usually are longer. It is also more limited in the classifications of malocclusion that can be addressed since force is not easily applied in all directions.
Dental researchers have long postulated that a pulsating force might be used to move teeth more rapidly and to ease the discomfort of traditional orthodontics, but Dr. Mao was probably the first to prove that cyclic forces improved and accelerated dental straightening (see U.S. Pat. No. 6,684,639, U.S. Pat. No. 6,832,912, U.S. Pat. No. 7,029,276). Certain dynamic loading patterns (cycling force with rest periods) were shown to greatly increase bone formation compared to basic dynamic loading. Inserting rest periods is now known to be especially efficacious as it allows mechano-sensitivity to be restored to the bone tissue. A point of diminishing returns is reached within each loading session. Therefore, intermittently loading cyclic force can increase the rate of bone formation significantly.
The early Mao and similar studies provided a basis for both possible efficacy and likely safety for using vibration in humans to assist orthodontic tooth movement, but the animal studies needed to be repeatable in humans, and the devices used by Mao and the others were completely unsuitable for human clinical use, involving clamping a rabbit head in a fixation device, and applied force to the cranium to assess sutural osteogenesis. Further, Mao used cyclic forces of 5 Newtons (N) and 0.2-1 Hz and such forces are probably too high for human use, both from comfort and root resorption perspectives.
OrthoAccel Technologies Inc., was the first to invent and clinically test a commercially successful dental vibrating device, as described in US2008227046 and related cases, designed to apply cyclic forces to the dentition for accelerated remodeling purposes. Both intra-oral and extra-oral embodiments are described in US2008227046, each having processors to capture and transmit patient usage information.
The bite plate was specially designed to contact occlusal as well as lingual and/or facial surfaces of the dentition, and thus was more effective than any prior art devices in conveying vibrational forces to the teeth, transmitting vibration in two axes. Further, the device was tested in clinical trials and was shown to speed orthodontic remodeling as much as 50%, and is truly a breakthrough in orthodontic technology (Kau 2010).
Finally, the device is slim, capable of hands free operation, lacks the bulky head gear of prior art devices, and has optimized force and frequency for orthodontic remodeling. Thus, its comfort level and compliance was also found to be high, with patients reporting that they liked the device, especially after the motor was redesigned to be quieter and smoother, as described in US2010055634 et seq. In fact, this device has been marketed as AcceleDent™ in the United States and several other countries and has achieved remarkable commercial success since its recent introduction. AcceleDent™ represents the first successful clinical approach to accelerate orthodontic tooth movement by modulating bone biology in a non-invasive and non-pharmacological manner.
During the 1960s, there was considerable interest in piezoelectricity as a stimulus for bone remodeling. This arose because it was noted that distortion of crystalline structures generated small electrical charges, which potentially may have been responsible for signaling bone changes associated with mechanical forces. Therefore, the interest in electricity and bone remodeling was considerable.
In 1980, Davidovitch et al. showed that cat teeth treated by force and electricity moved significantly faster than those treated by force alone. These results suggested that orthodontic tooth movement can be accelerated by the use of locally applied, small electric currents. Then in 1990, Hashimoto confirmed that cat teeth moved more rapidly under a 60 gram force combined with a one hertz square wave pulse of 6 volts, which induced a current of about 10 μAmp. However, no dedicated device was built by these researchers, who used an experimental set-up, completely inappropriate for human use.
In 1987, Stark tested a pulsed electromagnetic field (“PEMF”) in guinea pigs and found that significantly increased both the rate and final amount of orthodontic tooth movement observed over the 10-day experimental period. Thus, it has been shown that PEMF can be used in place of pulsed micro-currents, a result which is not surprising given that electromagnetic fields can induce current and vice versa.
In 1993, Rubin et al. showed in an in vivo model of osteopenia that the bone resorption that normally parallels disuse can be prevented or even reversed by the exogenous induction of electric fields. Importantly, the manner of the response (i.e., formation, turnover, resorption) was exceedingly sensitive to subtle changes in electric field parameters. Fields below 10 microV/cm, when induced at frequencies between 50 and 150 Hz for 1 hour/day, were sufficient to maintain bone mass even in the absence of function. Reducing the frequency to 15 Hz made the field extremely osteogenic. Indeed, this frequency-specific sinusoidal field initiated more new bone formation than a more complex pulsed electromagnetic field (PEMF), though inducing only 0.1% of the electrical energy of the PEMF. The frequencies and field intensities most effective in the exogenous stimulation of bone formation were similar to those produced by normal functional activity.
Researchers have attempted to develop a device to implement the Davidovitch micropulse method. U.S. Pat. No. 4,153,060 by Korostoff and Davidovitch, for example, describes an intraoral device wherein an anodic electrode is placed in the direction of applied force and a cathodic electronic on the opposite side of the tooth to be moved. However, being completely intraoral, complex and requiring semi-permanent attachment of electrodes, the device was impractical and never commercialized.
U.S. Pat. No. 4,854,865 was another attempt to capitalize on the Davidovitch research and develop a device suitable for orthodontic electro-osteogenesis. Another completely intraoral device is described in this patent, having an anode that is positioned against the epithelial gingiva, whilst a cathode is placed in engagement with epithelial gingiva at a position adjacent to the tooth to be repositioned, and electric current is applied between the cathode and anode. The device uses noble metals for both electrodes, and an electrolytic gel provides good conduction. This device is also less than practical, both because it targets one tooth at a time, but also because it placed the electricity generating portion of the device inside the mouth, which has limited room and raises the potential of shorts or leaks, and the resulting unpleasant consequences.
US20100082027 describes the use of microcurrent therapy to control oral inflammation where the frequency is 0.1-970 Hz and the amplitude from 20-400 microAmps. Although having a very different purpose, a device is described with external electrical pulse generator coupled to leads that attach to a patient's head and inside the patient's mouth. Therefore, this device is impractical or inappropriate for dental remodeling uses.
Thus, what are needed in the art are practical and safe devices that allow the safe and comfortable use of electro-osteogenesis to speed orthodontic remodeling.